The primary purpose of the proposed study is to conduct a rigorous outcome evaluation of a statewide randomized trial of alcohol interlock systems in the State of Maryland as a means of preventing recidivism in first-time DWI (Driving While Intoxicated) offenders. All first-time DWI offenders in Maryland will complete a State mandated diagnostic evaluation by the investigative team. Then all alcohol dependent/ abusive DWI offenders (estimated at 6,450 individuals) will be randomly assigned to Standard Treatment (T) or to an Ignition Interlock plus Treatment (IIT) condition that will be mandated by the Maryland Department of Motor Vehicles for 12 months. In addition to examining rates of DWI recidivism and interlock tampering and false start data, the current project will include confidential assessments of DWI risk behavior, alcohol use, social and psychological functioning at each of the three data collection points. Study participants will be assessed at baseline and at 12-month and 24-month follow-ups. The current project will be the first randomized Statewide trial of alcohol interlocks ever to be conducted, and is the second truly randomized trial of interlocks ever to be conducted (including any studies that are currently underway, such as Voas et al. in Canada). The first randomized trial of interlocks, also conducted by the proposed PI, was with multiple offenders in the State of Maryland (see Preliminary Studies section). This project is also the first study ever to assess the effects of treatment and treatment plus interlock on other variables such as alcohol use, self-reported rates of driving after drinking, and levels of psychological and social functioning over time as well as conventional outcomes such as re-arrest for DWI. In general, the proposed study will provide the first efficacy information available on utilizing ignition interlock systems with first time DWI offenders, and will allow for a detailed examination of which individuals respond best to the treatment conditions examined. The study will also be the first to provide an extensive description of first-time DWI offenders. It is also the first study to investigate possible unintended negative consequences of introducing alcohol interlocks (e.g., an increase in drinking when not driving, an increase in riding with intoxicated drivers, and a decrease in social functioning). It is also the first study to investigate the effects of interlocks as an adjunct to treatment in various racial/ethnic subpopulations, and in other subgroups. The proposed project takes advantage of a unique opportunity where State officials are willing to randomly assign all first-time "problem drinker", DWI offenders to participate in such a longitudinal study. If the project produces the anticipated effect in reducing DWI recidivism in first-time DWI offenders, this program could be immediately adopted by the State of Maryland, and could serve as a national model for DWI prevention.